diff --git a/src/main.c b/src/main.c
index 10a221d..283e113 100644
--- a/src/main.c
+++ b/src/main.c
@@ -78,6 +78,34 @@ static int posixly_correct = 0;
 static enum total_mode total_mode = TOTAL_AUTO;
 static const char *files_from = NULL; /* --files0-from=F, or NULL */
 
+/*
+ * LC_CTYPE handling.  A freshly exec'd process already runs in the C
+ * locale, so when the environment selects C/POSIX (or selects nothing)
+ * the setlocale() call is skipped: glibc would only re-derive the same
+ * state, at a cost measurable on the 1-line benchmark inputs.  When the
+ * locale really is multibyte we adopt it exactly like GNU does.
+ */
+static int in_c_locale; /* LC_CTYPE resolves to C/POSIX, or is unset */
+static int locale_done; /* setup_locale() has run */
+
+static void setup_locale(void)
+{
+    const char *v;
+
+    if (locale_done)
+        return;
+    locale_done = 1;
+    v = getenv("LC_ALL");
+    if (v == NULL || v[0] == '\0')
+        v = getenv("LC_CTYPE");
+    if (v == NULL || v[0] == '\0')
+        v = getenv("LANG");
+    in_c_locale = v == NULL || v[0] == '\0' || strcmp(v, "C") == 0 ||
+                  strcmp(v, "POSIX") == 0;
+    if (!in_c_locale)
+        setlocale(LC_CTYPE, "");
+}
+
 /* gnulib quote() style: locale quotation marks in a UTF-8 locale,
  * ASCII apostrophes elsewhere. Only argmatch diagnostics use it. */
 static int curly_quotes;
@@ -141,6 +169,30 @@ static void init_isprint_tab(void)
         isprint_tab[i] = isprint((unsigned char)i) ? 1 : 0;
 }
 
+/* The C/POSIX byte classes are fixed: isspace() is the six ASCII
+ * whitespace bytes and isprint() the range 0x20..0x7e.  Precomputing
+ * them skips 512 ctype() calls per exec in the common C-locale run. */
+static void init_ws_tab_c(void)
+{
+    int i;
+
+    memset(ws_tab, 0, sizeof ws_tab);
+    for (i = '\t'; i <= '\r'; i++)
+        ws_tab[i] = 1;
+    ws_tab[' '] = 1;
+    ws_tab[0xa0] = (unsigned char)!posixly_correct;
+    nbsp_ws = ws_tab[0xa0];
+}
+
+static void init_isprint_tab_c(void)
+{
+    int i;
+
+    memset(isprint_tab, 0, sizeof isprint_tab);
+    for (i = 0x20; i <= 0x7e; i++)
+        isprint_tab[i] = 1;
+}
+
 static void try_help(void)
 {
     fprintf(stderr, "Try 'fastwc --help' for more information.\n");
@@ -187,9 +239,19 @@ static void qfile(FILE *out, const char *s)
         fputs(s, out);
 }
 
-/* quote(): always-quoting locale style used by argmatch diagnostics. */
+/* quote(): always-quoting locale style used by argmatch diagnostics.
+ * The quote style is only needed on the --total error path, so the
+ * locale work stays out of every other invocation. */
 static void qarg(FILE *out, const char *s)
 {
+    static int qarg_ready;
+
+    if (!qarg_ready)
+    {
+        qarg_ready = 1;
+        setup_locale();
+        init_quote_style();
+    }
     fputs(curly_quotes ? "\xe2\x80\x98" : "'", out);
     fputs(s, out);
     fputs(curly_quotes ? "\xe2\x80\x99" : "'", out);
@@ -540,6 +602,34 @@ static count_lw_fn pick_kernel(void)
 }
 #endif
 
+/* One-time state the counting paths need, run after the options are
+ * known so --help/--version/usage errors pay none of it.  The locale is
+ * only locale-sensitive for -m/-w/-L, the per-byte tables only for word
+ * and -L counting, and the SIMD kernel only for byte-path counts. */
+static void init_count_state(void)
+{
+    if (flags & (F_CHARS | F_WORDS | F_MAXLEN))
+    {
+        setup_locale();
+        if (flags & F_WORDS)
+        {
+            if (in_c_locale)
+                init_ws_tab_c();
+            else
+                init_ws_tab();
+        }
+        if (flags & F_MAXLEN)
+        {
+            if (in_c_locale)
+                init_isprint_tab_c();
+            else
+                init_isprint_tab();
+        }
+    }
+    if (flags & (F_LINES | F_WORDS))
+        count_lw = pick_kernel();
+}
+
 /*
  * The Unicode white space set as GNU wc 9.11 sees it: glibc's iswspace()
  * (which omits the no-break spaces U+00A0, U+2007, U+202F) plus those
@@ -1413,16 +1503,10 @@ int main(int argc, char **argv)
     long n_args = 0;
     total_t totals = {0, 0, 0, 0, 0};
 
-    setlocale(LC_CTYPE, "");
     posixly_correct = getenv("POSIXLY_CORRECT") != NULL;
-    init_quote_style();
-    init_ws_tab();
-    init_isprint_tab();
-    count_lw = pick_kernel();
-    /* Line-buffer stdout like GNU, so parallel processes do not
-     * interleave their rows. */
-    setvbuf(stdout, NULL, _IOLBF, 0);
 
+    /* Option parsing needs no locale, so --help/--version and usage
+     * errors return before any of the one-time startup state exists. */
     while ((optc = getopt_long(argc, argv, "clLmw", longopts, NULL)) != -1)
         switch (optc)
         {
@@ -1469,6 +1553,11 @@ int main(int argc, char **argv)
     if (flags == 0)
         flags = F_LINES | F_WORDS | F_BYTES; /* wc default: -l -w -c */
 
+    /* Line-buffer stdout like GNU, so parallel processes do not
+     * interleave their rows. */
+    setvbuf(stdout, NULL, _IOLBF, 0);
+    init_count_state();
+
     if (files_from)
     {
         FILE *stream;
@@ -1908,7 +1997,11 @@ int main(void)
     /* The CLI build's helpers are compiled out of reach here. */
     (void)usage;
     (void)try_help;
+    (void)setup_locale;
     (void)init_isprint_tab;
+    (void)init_isprint_tab_c;
+    (void)init_ws_tab_c;
+    (void)init_count_state;
     (void)init_quote_style;
     (void)qaf;
     (void)qfile;